There are conventionally-known microscopes using a sheet illumination method in which excitation light focused in the form of a plane by an illumination optical system is made incident on a specimen along an incident plane intersecting the optical axis of a detection optical system that detects fluorescence from the specimen (for example, see PTL 1). In an epi-illumination method or a transmitted illumination method, excitation light focused at a single point or a plurality of points is two-dimensionally scanned, thereby acquiring a two-dimensional image. According to the sheet illumination method, a wide area can be illuminated at one time, and only an area in which excitation light is focused in a focal plane of the detection optical system is illuminated, thus making it possible to reduce the time required to acquire an image.